Such devices (which are intended to enable a vehicle whose wheels are fitted therewith to conserve sufficient driveability or mobility in the event of a reduction in tire pressure) are fitted, in particular, to the wheels of military vehicles. Numerous embodiments of such devices exist, and by way of example, mention may be made of those described in FR-A-2 246 405 which are constituted by a ring of rubber of dimensions such that after being installed inside the tire cover to which it is fitted, it forces the beads of the cover against the flanges of the rim, thereby preventing the cover from moving relative to the rim in the event of a drop in the inflation pressure of the tires, which may be done voluntarily, e.g. to cross certain types of terrain. Although they are satisfactory, such devices are nevertheless not easy to install and it is necessary to make use of straps with ratchets for deforming the ring and positioning it inside the cover. The non-negligible weight of the solid ring of rubber fitted with cording has an unfavorable effect on the characteristics of a vehicle when all of its wheel are fitted therewith.